1. Field of the Invention
This invention relates to a light emitter including an organic material such as an organic semiconductor.
2. Description of the Related Art
C. W. Tang et al. reported an electroluminescent (EL) device which uses an organic material as a light emitting element (C. W. Tang et al. Appl. Phys. Lett. Vol. 51, p. 913, 1987).
The Tang""s EL device includes a glass substrate coated with a film of indium tin oxide (ITO). A first organic layer of an aromatic diamine extends on the ITO film. A second organic layer extends on the first organic layer. The second organic layer is a luminescent film which belongs to a class of fluorescent metal chelate complexes. An example thereof is 8-hydroxyquinoline aluminum (Alq3). A top electrode extends on the second organic layer. The top electrode is an alloy or mixture of magnesium (Mg) and silver (Ag). A direct-current power source is connected between the ITO film and the top electrode. The ITO film serves as an anode while the Mg:Ag electrode operates as a cathode. In the Tang""s EL device, efficient injection of holes and electrons is provided from the ITO anode and the Mg:Ag cathode. Electron-hole recombination and green electroluminescent emission are confined near the organic interface region. A high external quantum efficiency (1% photon/electron), a high luminous efficiency (1.5 lm/W), and a great brightness ( greater than 1000 cd/m2) are achievable at a driving voltage below 10 V.
Some prior-art light emitters including organic layers are equipped with optical microcavities for narrowing spectrum widths of emitted light.
There are known organic light emitters which have waveguiding arrangements and light-amplifying structures.
It is an object of this invention to provide an improved organic light emitter.
A first aspect of this invention provides an organic light emitter comprising an anode; a cathode; a first layer of organic material which includes a light emitting layer, and which extends between the anode and the cathode; a second layer having a refractive index higher than a refractive index of the light emitting layer; a substrate; and means for optically coupling the second layer and the light emitting layer to cause an optical waveguide which propagates light generated by the light emitting layer along a direction parallel to a surface of the substrate; wherein at least part of the optical waveguide has an effective refractive index which spatially and periodically varies in a direction parallel to the surface of the substrate.
A second aspect of this invention provides an organic light emitter comprising an anode; a cathode; a first layer of organic material which includes a light emitting layer, and which extends between the anode and the cathode; a substrate; and a second layer having a refractive index higher than a refractive index of the light emitting layer, and being optically coupled to the light emitting layer to cause an optical waveguide which propagates light generated by the light emitting layer along a direction parallel to a surface of the substrate; wherein at least part of the optical waveguide has an effective refractive index which spatially and periodically varies in a direction parallel to the surface of the substrate to cause an optical resonator operating on the light generated by the light emitting layer.
A third aspect of this invention provides an organic light emitter comprising an anode; a cathode; a first layer of organic material which includes a light emitting layer, and which extends between the anode and the cathode; a substrate; and a second layer having a refractive index higher than a refractive index of the light emitting layer, and being optically coupled to the light emitting layer to cause an optical waveguide which propagates light generated by the light emitting layer; wherein the second layer includes at least first and second regions separate from each other, and the first region has an effective refractive index which spatially and periodically varies at a first predetermined period, and the second region has an effective refractive index which spatially and periodically varies at a second predetermined period different from the first predetermined period.
A fourth aspect of this invention is based on the first aspect thereof, and provides an organic light emitter wherein an optical length corresponding to a period of the variation in the effective refractive index of the optical waveguide is equal to an integer multiple of a half of a wavelength of the light generated by the light emitting layer.
A fifth aspect of this invention is based on the fourth aspect thereof, and provides an organic light emitter wherein the optical length corresponding to the period of the variation in the effective refractive index of the optical waveguide is equal to the half of the wavelength of the light generated by the light emitting layer.
A sixth aspect of this invention is based on the fourth aspect thereof, and provides an organic light emitter wherein the optical length corresponding to the period of the variation in the effective refractive index of the optical waveguide is equal to the wavelength of the light generated by the light emitting layer.
A seventh aspect of this invention is based on the first aspect thereof, and provides an organic light emitter wherein the optical waveguide is adjacent to the light emitting layer, and one of the anode and the cathode includes a transparent electrode, and the light generated by the light emitting layer is outputted to an external via the transparent electrode, and the outputted light forms a beam having a plane shape.
An eighth aspect of this invention provides an organic light emitter comprising an anode; a cathode; a layer of organic material which includes a light emitting layer, and which extends between the anode and the cathode; a substrate; and a transparent layer being adjacent to and optically coupled to the light emitting layer and having a refractive index which is higher than a refractive index of the light emitting layer to cause an optical wavelength; wherein the refractive index of the transparent layer spatially and periodically varies, and the optical waveguide propagates light emitted by the light emitting layer and has an effective refractive index which spatially and periodically varies in a direction parallel to a surface of the substrate in accordance with the spatial periodic variation in the refractive index of the transparent layer.
A ninth aspect of this invention is based on the eighth aspect thereof, and provides an organic light emitter wherein the transparent layer includes one of the anode and the cathode, and has a composition which spatially and periodically varies in a predetermined direction with respect to the transparent layer.
A tenth aspect of this invention is based on the eighth aspect thereof, and provides an organic light emitter wherein the transparent layer includes one of the anode and the cathode, and has a thickness which spatially and periodically varies in a predetermined direction with respect to the transparent layer.
An eleventh aspect of this invention provides an organic light emitter comprising an anode; a cathode; a layer of organic material which includes a light emitting layer, and which extends between the anode and the cathode; a substrate; a first transparent layer being adjacent to the light emitting layer and having a refractive index which is higher than a refractive index of the light emitting layer; and a second transparent layer having a refractive index which spatially and periodically varies; wherein the first and second transparent layers cause an optical waveguide, and the optical waveguide propagates light emitted by the light emitting layer and has an effective refractive index which spatially and periodically varies in a direction parallel to a surface of the substrate in accordance with the spatial period variation in the refractive index of the second transparent layer.
A twelfth aspect of this invention provides an organic light emitter comprising an anode; a cathode; a transparent electrode including one of the anode and the cathode; a layer of organic material which includes a light emitting layer, and which extends between the anode and the cathode; a substrate; and a transparent layer extending between the transparent electrode and the light emitting layer, and having a refractive index which is higher than a refractive index of the light emitting layer to cause an optical waveguide; wherein the refractive index of the transparent layer spatially and periodically varies, and the optical waveguide propagates light emitted by the light emitting layer and has an effective refractive index which spatially and periodically varies in a direction parallel to a surface of the substrate in accordance with the spatial periodic variation in the refractive index of the transparent layer.
A thirteenth aspect of this invention is based on the twelfth aspect thereof, and provides an organic light emitter wherein the transparent electrode has a refractive index higher than a refractive index of the light emitting layer.
A fourteenth aspect of this invention is based on the eleventh aspect thereof, and provides an organic light emitter wherein the second transparent layer includes a film of organic material, and the organic material film has a composition which spatially and periodically varies in a predetermined direction with respect to the organic material film.
A fifteenth aspect of this invention is based on the eleventh aspect thereof, and provides an organic light emitter wherein the second transparent layer includes a dielectric layer, and the dielectric layer has a composition which spatially and periodically varies in a predetermined direction with respect to the dielectric layer.
A sixteenth aspect of this invention is based on the eleventh aspect thereof, and provides an organic light emitter wherein the second transparent layer includes a dielectric layer, and the dielectric layer has a thickness which spatially and periodically varies in a predetermined direction with respect to the dielectric layer.
A seventeenth aspect of this invention is based on the eleventh aspect thereof, and provides an organic light emitter wherein the second transparent layer includes a plurality of dielectric layers, and at least one of the dielectric layers has a thickness and a composition one of which spatially and periodically varies in a predetermined direction with respect to the dielectric layer.
An eighteenth aspect of this invention is based on the third aspect thereof, and provides an organic light emitter wherein the second layer includes first, second, and third regions separate from each other, and the first region has an effective refractive index which spatially and periodically varies at a first predetermined period corresponding to a wavelength of red light, and the second region has an effective refractive index which spatially and periodically varies at a second predetermined period corresponding to a wavelength of green light, and the third region has an effective refractive index which spatially and periodically varies at a third predetermined period corresponding to a wavelength of blue light.
A nineteenth aspect of this invention provides an organic light emitter comprising an anode; a cathode; a first layer of organic material which includes a light emitting layer, and which extends between the anode and the cathode; a second layer having a refractive index higher than a refractive index of the light emitting layer to cause an optical waveguide for propagating light generated by the light emitting layer; and a portion for enabling a density of a current in the light emitting layer to periodically vary in a spatial domain.
A twentieth aspect of this invention provides an organic light emitter comprising an anode; a cathode; a first layer of organic material which includes a light emitting layer, and which extends between the anode and the cathode; an optical waveguide for propagating light generated by the light emitting layer; and a portion for enabling a density of a current in the light emitting layer to periodically vary in a spatial domain; wherein an effective refractive index of the optical waveguide spatially and periodically varies in accordance with the spatially periodic variation in the current density so that an optical resonator is caused which operates on the light generated by the light emitting layer.
A twenty-first aspect of this invention provides an organic light emitter comprising an anode; a cathode; a first layer of organic material which includes a light emitting layer, and which extends between the anode and the cathode; a substrate; a second layer optically coupled to the light emitting layer and having a refractive index higher than a refractive index of the light emitting layer to cause an optical waveguide for propagating light generated by the light emitting layer in a direction parallel to a surface of the substrate; and a portion for enabling a density of a current in the light emitting layer to periodically vary in a spatial domain.
A twenty-second aspect of this invention is based on the twentieth aspect thereof, and provides an organic light emitter wherein an optical length corresponding to a period of the variation in the effective refractive index of the optical waveguide is equal to an integer multiple of a half of a wavelength of the light generated by the light emitting layer.
A twenty-third aspect of this invention is based on the twentieth aspect thereof, and provides an organic light emitter wherein the optical length corresponding to the period of the variation in the effective refractive index of the optical waveguide is equal to the wavelength of the light generated by the light emitting layer.
A twenty-fourth aspect of this invention is based on the nineteenth aspect thereof, and provides an organic light emitter wherein one of the anode and the cathode includes a transparent electrode, and the light generated by the light emitting layer is outputted to an external via the transparent electrode, and the outputted light forms a polarized beam.
A twenty-fifth aspect of this invention is based on the nineteenth aspect thereof, and provides an organic light emitter wherein the portion includes the cathode which has a spatially periodic structure.
A twenty-sixth aspect of this invention is based on the twenty fifth aspect thereof, and provides an organic light emitter wherein the second layer includes a transparent dielectric layer.
A twenty-seventh aspect of this invention is based on the twenty-fifth aspect thereof, and provides an organic light emitter wherein the second layer includes a transparent electrode forming the anode.
A twenty-eighth aspect of this invention is based on the nineteenth aspect thereof, and provides an organic light emitter wherein the portion includes the anode which has a spatially periodic structure.
A twenty-ninth aspect of this invention is based on the twenty-eighth aspect thereof, and provides an organic light emitter wherein the second layer includes a transparent dielectric layer.
A thirtieth aspect of this invention is based on the twentyeighth aspect thereof, and provides an organic light emitter wherein the second layer includes a transparent electrode forming the anode.
A thirty-first aspect of this invention is based on the nineteenth aspect thereof, and provides an organic light emitter wherein the portion includes current blocking segments extending between the anode and the cathode, and spaced at a predetermined period.
A twenty-second aspect of this invention is based on the thirty-first aspect thereof, and provides an organic light emitter wherein the second layer includes a transparent dielectric layer.
A thirty-third aspect of this invention is based on the nineteenth aspect thereof, and provides an organic light emitter wherein the portion includes a plurality of different regions for enabling the current density to vary in the spatial domain at different periods respectively.
A thirty-fourth aspect of this invention is based on the nineteenth aspect thereof, and provides an organic light emitter wherein the portion includes first, second, and third regions separate from each other, the first region enabling the current density to vary in the spatial domain at a first predetermined period corresponding to a wavelength of red light, the second region enabling the current density to vary in the spatial domain at a second predetermined period corresponding to a wavelength of green light, the third region enabling the current density to vary in the spatial domain at a third predetermined period corresponding to a wavelength of blue light.
A thirty-fifth aspect of this invention is based on the thirty-third aspect thereof, and provides an organic light emitter wherein the optical waveguide is formed with current injection regions having periods in different directions respectively.